Palaeospondylus gunni, a small creature with an eel-like body that lived 390 million years ago, is one of the most enigmatic fossil vertebrates, and its phylogenetic position has remained unclear since its discovery in Scotland in 1890.
Palaeospondylus gunni is a mysterious fish-like fossil vertebrate with a strange set of morphological features, including a lack of teeth and dermal bones in the fossil record.
The small animal with an eel-like body lived during the Middle Devonian period, approximately 390 million years ago.
Despite its age, its position on the evolutionary tree has remained unclear, until now.
“Palaeospondylus gunni has baffled scientists since its discovery in 1890 as a puzzle that’s been impossible to solve,” said Dr. Daisy (Yuzhi) Hu, a researcher in the Department of Materials Physics at the Australian National University.
In the new research, Dr. Hu and colleagues analyzed cranial skeletons of Palaeospondylus gunni at the histological level three-dimensionally by using synchrotron radiation X-ray micro-computed tomography.
“Morphological comparisons of this animal have always been extremely challenging for scientists,” Dr. Hu said.
“However, recent improvements in high resolution 3D segmentation and visualization have made this previously impossible task possible.”
“Finding a specimen as well preserved as the ones we used is like winning the lottery, or even better!”
The researchers found that Palaeospondylus gunni was most likely a member of Sarcopterygii, a group of lobe-finned fishes, due to its cartilaginous skeleton and the absence of paired appendages.
“Despite the investigation, it is still hard to determine what the animal was with 100% accuracy,” Dr. Hu noted.
The findings mean that scientists could unlock a range of unknown morphological features and evolutionary history of four-limbed animals.
“Even with this new information, long-lasting investigations with the joint effort of scientists from around the world is needed to give us the perfect answer of what actually is Palaeospondylus gunni,” Dr. Hu said.
The results were published in the journal Nature.
T. Hirasawa et al. Morphology of Palaeospondylus shows affinity to tetrapod ancestors. Nature, published online May 25, 2022; doi: 10.1038/s41586-022-04781-3
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